The present invention relates to light-emitting diode lamps and light-emitting diode display devices, which are used for, for example, LED (light-emitting diode) display boards for outdoor purpose. They are suitably used for a road information display of traffic information and so on, an outdoor display for advertisement and publicity, or a traffic signal and so on.
Conventionally, there has been an LED lamp as shown in FIG. 16. In the LED lamp, an LED chip 102 is mounted on a lead frame 101 and resin-molded to be embedded in a resin lens 103. The resin lens 103 has a curved surface 103A which is curved in a convex shape toward the light-emitting direction of the LED chip 102.
When the LED lamp shown in FIG. 16 is used for, for example, an outdoor LED display board, sunlight directly enters the LED lamp in the early morning or in the late afternoon since the irradiation angle of sunlight is small. As the result, there is a phenomenon that the unlit LED lamp looks as if it were lighting. The phenomenon disadvantageously reduces the contrast ratio between the lighting LED lamp and the unlit LED lamp, and therefore it becomes sometimes difficult to see the LED display board. The phenomenon resembles misrecognition of the traffic signal due to the west sun, and this significantly degrades the display quality of the LED display board that constitutes the electronic display board or the like.
The phenomenon in the conventional LED lamp is described more in detail with reference to FIG. 18. The irradiation angle of sunlight rays is small 111a and 111b in the early morning or in the late afternoon. If sunlight rays (e.g., west sun light) are incident on the resin lens 103 as shown in FIG. 18, then the light rays are refracted at a curved surface 103A of the resin lens 103. Thereby, their traveling directions of light come closer to normal lines L101 and L102 at incident points P101 and P102, respectively. The sunlight rays 111a and 111b are incident on an LED chip mounting portion 101A of the lead frame 101 due to the refraction, and reflected thereon. Then, the sunlight rays 111a and 111b are incident on and refracted at the curved surface 103A of the resin lens 103 at an incident angle roughly close to that of the emission light of the LED chip 102, and thereafter emitted at an angle close to that of an outgoing beam axis J101. This is the phenomenon that the unlit LED lamp looks as if it were lighting.
Next, FIG. 17 shows another prior art example. The prior art example has a structure similar to that of the foregoing prior art example, where the LED chip 102 is mounted on the lead frame 101. However, this prior art example differs from the foregoing prior art example in having upper and lower curved surfaces 104A and 104B of different configurations.
In this prior art example, the curved surface 104A and the curved surface 104B are located on one side and the other side respectively with relation to a plane that does not cross the center of the light-emitting surface of the LED chip 102. This makes it possible to prevent the concentration of the outgoing beam of the light-emitting diode chip on the plane that penetrate the center of the light-emitting surface, and therefore prevent the occurrence of a distorted light emission peak on the front surface. Thereby, it is possible to avoid a phenomenon that the light emission intensity is sharply reduced only when the viewpoint is slightly shifted from the front surface.
However, this prior art example has consumed a lot of cost and time in production because complicated simulations and trial evaluations must be repeated for an appropriate lamp configuration every time the dimension of lamp is changed.
As described above, the firstly-stated prior art example needs to examine a place where the LED display board is installed because it cannot be installed in the place exposed to the west sun or must be installed there with the screen of the LED display board inclined downward. Therefore, it is sometimes impossible to apply the firstly-stated prior art to the display utilized for traffic safety particularly in the traffic information board or the like, which display is one of the original purposes of the firstly-stated prior art.
In the secondly-stated prior art example, the combination lens of the upper and lower portions having different curvatures repeatedly has required the complicated simulations and the trial evaluations for an appropriate configuration of lamp every time the dimension thereof is changed, which have consumed a lot of cost and time for developing new models.
JP 2004-104077 A and JP H11-154766 A are given as the prior art reference documents.